Measuring blood pressure information is important for keeping track of the health state of a measurement subject. Various types of blood pressure information can be measured by using a blood pressure information measurement apparatus. A blood pressure information measurement apparatus includes a cuff, and a pressure pump and discharge valve are used as a pressure increase/reduction mechanism for increasing and reducing the internal pressure of the cuff. In a closed state, the discharge valve maintains the internal pressure of a fluid bladder whose pressure has been increased by the pressure pump, and in an open state, the discharge valve reduces the pressure.
A flow rate control valve can be suitably used as the discharge valve. The flow rate control valve includes a movable shaft and a valve body that opposes an outflow port. The valve body is provided at an end portion of the movable shaft. When the internal pressure of the cuff is to be reduced, the outflow flow rate can be controlled by variably controlling the distance between the outflow port and the valve body using the variable shaft. This kind of flow rate control valve largely comes in two types: linear and solenoid.
The solenoid type includes a plunger (movable iron core) serving as a movable shaft, a core (fixed iron core) provided with an outflow port, and a solenoid coil, and the plunger is moved using the solenoid coil. Unlike the linear type, the solenoid type does not require a permanent magnet and has a simple configuration and thus can be made lighter and smaller, and thus the solenoid type is advantageous in that the manufacturing cost is easily reduced.
JP 2014-055607A (Patent Literature 1) discloses a solenoid-type flow rate control valve. This flow rate control valve includes a core provided with an outflow port, a bobbin, a plunger arranged inside of the bobbin, and a valve body provided at an end portion of the plunger so as to oppose the outflow port. If the valve body is in contact with the core, the outflow port is closed by the valve body. If the valve body is separate from the core, air is discharged to the outside of the flow rate control valve via a gap between the inner circumferential surface of the bobbin and the outer circumferential surface of the plunger.
JP H02-131405U (Patent Literature 2) discloses a utility model relating to a gas flow valve. This gas flow valve includes a housing having a cylindrical shape and a valve body arranged inside of the housing. A recess is provided inside of the housing. One side of the recess has a linear shape, and when the valve body is inserted into the housing, a gap is formed between the inner wall (linear portion) of the housing and the valve body. This gap functions as a gas flow path, and according to Patent Literature 2, there may be one, two, three, or more of these gas flow paths.